The invention relates generally to the detection and reporting of a power failure, and more particularly, to a method and apparatus for anticipating the loss of power at a load prior to the time at which the power failure at the load has deleterious effects upon equipment performance.
Electronic equipment, for example electronic computers, have always been particularly sensitive to the power-on and power-off sequences to which their components are subjected. During the power-on sequence, for example, a computer must be held in a static, initial condition, until its power source has become stable. Similarly, during the power-off sequence, the computer must be constrained to prevent unpredictable operation, or corruption or distortion of stored information.
Of all of the power failure conditions to which electronic equipment can be subjected, the loss or degradation of DC power to a computer's circuits is perhaps the most traumatic. That loss or degradation of power, if not detected promptly and dealt with accordingly, can adversely affect not only ongoing computations, but can further cause changes in, or loss of, memory. In either instance, there can be a severe interruption to the computation process even after the power has been restored.
Accordingly, therefore, most sophisticated electronic devices provide for a regulated power supply in which the voltage applied to the electronic circuitry, the load, is continuously monitored to avoid changes in the voltage applied to the load, even though the input voltage to the equipment, the line voltage power source, may vary by, for example, twenty percent. These regulated voltage power supplies, which can be for example of the switching-type, thus typically monitor the load voltage to detect a power failure. However, by the time the circuitry detects the occurrence of a power failure, there is very little time available to take the necessary steps to prevent the power failure from potentially causing a major interruption to the processing being performed by the electronic circuitry.
Accordingly, therefore, an object of the present invention is a method and apparatus which enables the power failure detection circuitry to anticipate the occurrence of a power failure at the load, thereby providing additional time for the equipment to react to the power failure, and therefore avoid the likelihood of severe unpredictable disruptions to signal processing and to allow normal resumption of the processing when power is restored. Other objects of the invention are a method and apparatus for detecting a power failure which are reliable, which are simple in circuit implementation, which adjust automatically to degradation of components in the voltage regulation circuitry, and which can be adapted to equipment with substantially little modification of the existing circuitry.